1. Field
One embodiment of the invention relates to a storage device using a nonvolatile cache memory and a control method thereof, and the storage device capable of realizing low power consumption and high-speed read/write operation is configured to eliminate in particular storage errors of important data.
2. Description of the Related Art
In recent years, a storage device on which both of a memory card which is a semiconductor storage medium and a hard disk (HD) drive using a hard disk which is a magnetic storage medium can be mounted is developed (refer to Jpn. Pat. Appln. KOKAI Publication No. 2004-055102). For example, data of the memory card fetched from the exterior can be backed up into the hard disk (HD) which is a magnetic storage medium. Further, data of a hard disk (HD) can be transferred to the memory card and can be thus taken out.
As a mobile storage device, a storage device using a flash memory is developed (refer to Japanese Patent Publication No. 3407317). A large number of errors occur in the flash memory when the number of erase operations of the flash memory becomes large (for example, 100,000 times), and therefore, an attempt is made to solve the above problem. For example, a data management method for suppressing the number of erase operations for a specified area from becoming larger is provided.
As described above, there are devices using a plurality of various types of recording media, however, each of them has drawback and advantage. Although semiconductor devices such as memory card and flash memory have low power consumption and high write speed, they are unsuitable for storing large volumes of data. On the other hand, the hard disk is suitable for storing large volumes of data for a long time, but is inferior to semiconductor devices in low power consumption and high-speed data writing.